The present invention relates to a knock control apparatus and method for an internal combustion engine and contemplates controlling the ignition timing, supercharge pressure or the like of the engine in response to the occurrence of engine knocking.
In a knock control apparatus of this type, a knock discrimination level V.sub.L is generally produced by multiplying a knock sensor signal average level V.sub.MEAN by an adaptation constant K and then adding an offset value O.sub.S to the product, thereby obtaining V.sub.L =KxV.sub.MEAN +O.sub.S (e.g., U.S. Pat. No. 4,423,621). However, the above-mentioned conventional apparatus is disadvantageous in that due to the variations in characteristics among different engines or knock sensors caused during their manufacture, aging of the engine or the knock sensor or the like, the output of the knock sensor is varied and hence the required adaptation factor (required K-value) is varied, thereby causing the control knock sound to vary.
Also, particularly in the case of the known apparatus of the type which employs amplifiers having a plurality of amplification factors for knock sensor signal amplifying purposes so as to selectively use the amplification factors in accordance with the magnitude of a knock sensor signal or the like, the above-mentioned problem becomes more manifest. One of the causes for this problem is the offset value O.sub.S, for the offset value O.sub.S is a constant value. Thus, it is evident that the required K-value is varied by, for example, the amplification factor of a knock sensor signal.